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I'm not sure how to describe this problem. I'm fixing a puncture on my bike which is a road bike that requires pumping up to about 90psi.

So I fix the puncture, and I pump it up. At first it's okay, but within about maybe 5 minutes suddenly the valve starts releasing air.

I take the tube out, there's no puncture, I pump it up a little bit, it doesn't deflate. I put it back in the wheel and try again. Same again.

It's weird becuase if there was a faulty valve, wouldn't it leak air like all the time and straight away? Not like 5 minutes after I pump it up.

So is my valve busted and I should just get a new tube or is there something I can do to fix it?

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it's a schraeder valve –  Diskdrive Mar 24 '12 at 5:11
    
The simple fix (if it's not a hole in the tube) is to install a valve cap, preferably a metal one with a gasket inside. Probably available at an auto parts place. –  Daniel R Hicks Mar 24 '12 at 11:57
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1 Answer

up vote 2 down vote accepted

It sounds like either the valve core is slightly loose, which you can correct by tightening it with a valve core tool, or that the valve core seal is leaking, in which case you can replace the core, which may work, or the tube which is your pretty much guaranteed fix.

Valve Core Tool

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The actual core tool is the little forked thing on the upper right. Some metal valve caps come with this tool on them -- probably a little hard to find anymore, but should be still available. They're handy to have on the road to tighten cores (if you have Schraeder valves) and to let you quickly deflate a tube. –  Daniel R Hicks Mar 24 '12 at 11:56
    
True, and thanks for the clarification. This was the best photo I could find. –  zenbike Mar 24 '12 at 12:08
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